This research will attempt to define more clearly the role of the anti-Fc antibodies (rheumatoid factors) and the anti-Fab antibodies (serum agglutinators) in immunity. The rheumatoid factors do not appear to be related to elevated titers of serum agglutinators, although both may appear almost simultaneously in organ transplant rejection. These studies will be a continuation of work in progress that has shown the association of the serum agglutinators with severe supprative infection, has established the specificity of the agglutinators, has demonstrated these antibodies in transplant rejection and defined and characterized many of their properties.